ABUJA: Africa's most populous nation Nigeria was on Monday declared officially Ebola free but warned that it remained vulnerable as long as the virus was raging elsewhere in west Africa.
The country representative of the World Health Organisation, Rui Gama Vaz, said 42 days -- or two incubation periods of 21 days -- had elapsed without any new confirmed cases of the deadly virus.
"The virus is gone for now. The outbreak in Nigeria has been defeated," he told a news conference in Abuja alongside the country's health minister and survivors of the disease.
"This is a spectacular success story that shows to the world that Ebola can be contained."
Nigeria's official Ebola-free status comes after Senegal was given the all-clear on Friday, providing rare good news in the world's worst outbreak of the hemorrhagic fever.
More than 4,500 people have died this year and nearly 10,000 have been infected, most of them in Guinea, Liberia and Sierra Leone.
Senegal had one confirmed case, while Nigeria saw seven deaths from 19 confirmed cases according to latest WHO figures.
Both countries are now coming under close scrutiny as public health specialists around the world look to contain the spread of the disease after cases in Spain and the United States.
The WHO said developing countries and wealthier nations concerned about Ebola "may have something to learn" from the response of Nigeria and Senegal.
But Vaz also said that neither country could lower its guard, given that the epidemic had not been contained elsewhere in west Africa.
"We must be clear that we only won a battle. The war will only end when west Africa is also declared free of Ebola," he added.
"While the outbreak is now officially over, Nigeria's geographical position and extensive borders makes the country vulnerable to additional imported cases of Ebola virus disease."
Continued vigilance was required, as well as "strict compliance" with WHO preparation guidelines in the event of further cases, he added.
Ebola's arrival in Nigeria -- Africa's leading economy and top oil producer -- sparked fears of its rapid spread in the overcrowded megacity of Lagos, which is home to 20 million, and beyond.
The first case involved a Liberian finance ministry official, Patrick Sawyer, who was taken straight to a private hospital from Lagos airport after arriving visibly ill on a flight from Monrovia.
But the doomsday scenario did not happen. Doctors at the hospital physically restrained Sawyer from leaving and potentially spreading the virus across the city.
Once Sawyer was diagnosed and later died on July 25, a comprehensive contact tracing plan -- using an existing mapping programme for a mass outbreak of polio -- swung into action.
Some 1,800 staff were mobilised and trained to trace and monitor those at risk, as well as decontaminate infected places and care for the sick.
Nearly 900 people at risk in Lagos and the key oil hub of Port Harcourt were tracked down and checked twice a day for signs of the disease. Potential cases were isolated rapidly.
As well as rigorous contact tracing and a massive public awareness campaign, Nigeria introduced stringent health screening checks at all airports and seaports for arrivals and departures.
Cameroon shut its western border with Nigeria as a precaution, but Nigeria itself did not close its frontiers.
Travel bans were not imposed, although leading carrier Arik Air did suspend its scheduled routes to Liberia and Sierra Leone, which with Guinea have been the worst affected by Ebola.
The WHO said "strong leadership and effective coordination" was key to containing the outbreak, despite Nigeria facing an Islamist insurgency and serious health sector challenges.
"If a country like Nigeria... can do this... any country in the world experiencing an imported case can hold onward transmission to just a handful of cases," said WHO director-general Margaret Chan.